Author Topic: Making A Twin  (Read 1441 times)

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Offline 660magnum

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Making A Twin
« on: February 11, 2012, 04:28:34 pm »
I have a automotive machine shop friend in Idaho who flies model airplanes. He also sometimes makes up engines using parts of existing engines with custom crankcases, changing from piston ported to reed valve etc. He also converts glow fueled engines to ignition running gasoline with custom sensor and Walbro carb mounts and manifolds.

After making a couple 50 and 55cc reed valve singles, his latest project is a 60cc twin using existing available 30cc single parts.

Here is the engine partially assembled



He has purchased mufflers made by another gentleman



The drive hub, reed pyramid assembly, and carb are from existing available parts.



He has made the crankcase and adapted some of the purchased parts.

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Offline 660magnum

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Re: Making A Twin
« Reply #1 on: February 11, 2012, 04:37:47 pm »
He made the crankshaft from two existing 30cc cranks. The rear one is another front one that is cut off at the back bearing. He pushed the crank pins out, made a round center disk, and pushed in new hardened crank pins with the rods attached to make the twin crankshaft assembly.



Here is a view of the original crank assembly



The purchased piston for the 30cc engine



The purchased cylinder

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Offline 660magnum

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Re: Making A Twin
« Reply #2 on: February 11, 2012, 04:50:10 pm »
The cylinders and cranks are $40 ea

The pistons are $10ea and the rings are $5ea

The drive hub is $16

Main bearings were $30 for all three

The needle bearings for the wrist pins were $3 ea

The carb $40 and reed block $15

That comes out around $300 and then you have the aluminum block for the crankcase and black plate and the steel plate for the crankshaft joiner. And a lot of labor and amortization of machines and shop space.

This gentleman has saved some twisted crankshafts for me by re-aligning them.
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Offline 660magnum

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Re: Making A Twin
« Reply #3 on: February 11, 2012, 09:10:51 pm »
These cylinders use NGK CM-6 (Honda generator) spark plugs.

The complete ignition system including the spark plugs would be about $75

Then you will need a $25 battery, a $12 switch and wiring harness, and a battery charger for the ignition.
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Offline Cut4fun .

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Re: Making A Twin
« Reply #4 on: February 11, 2012, 09:16:32 pm »
Is that the twin that you had over here?  Maybe you didnt have a twin and my memory is just that bad.  :P
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Offline 660magnum

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Re: Making A Twin
« Reply #5 on: February 11, 2012, 10:07:20 pm »
The twin that I have (and I don't think I brought it over to your house - I mentioned it) is made from two Dolmar 111/115 cylinder/piston assemblies.

Remind me the next time I come over and I can bring it and the single.

They were manufactured by a small outfit called Brison. The single I have has never been run.

Brison 3.2 single and 6.4 twin
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Offline Al Smith

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Re: Making A Twin
« Reply #6 on: February 12, 2012, 07:39:41 pm »
Off all the proceedure in my opinion aligning the crankshft would be the most difficult part .

On a Harley crank it's relatively simple  .You just chuck it between centers in a lathe and use dial indicaters  and wedges and c-clamps and tighten up the pin nuts .

With a hard pressed crank you'd about  have to have each section perfect I would think before you pressed it .I've never seen it done so I have no idea how they do it .Just seems like a bear to me .

Offline 660magnum

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Re: Making A Twin
« Reply #7 on: February 13, 2012, 09:28:43 am »
I received a note from Richard about the engine that it is . . . . "now polished and painted and finished assembled. So far so good. I will hopfully get the rest of my parts in this next week. Oh The hub is a one of a kind deal since I will be swinging larger props I used the 55 hub size and bolt pattern, then necked it down to the 30 to match the case size. The retaining nut I made from a grade 8 bolt and I will never do that again, darn thing ruined a brand new made in the USA Tap a very spendy tap at that *L*  "

(He was talking about ruining his new tap while making the barrel nut that holds the prop drive hub onto the crankshaft)
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Offline Cyberwolf

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Re: Making A Twin
« Reply #8 on: February 14, 2012, 12:32:39 pm »
Hello I am Jims friend in Idaho that is making this engine, Jim asked me about how to realign crankshafts.
I thought I would post this here for all to see.
There are a couple of ways that I know of depending on just how badly tweeked they are tells me which way I want to start.
The first is to use a Milling Machine vise and clamp the counterweigths together to pull them back inline with each other, If the counterweigths are machined round on the rod end when the counterweigth was turned, I clamp them in several places then check with the following method. Sometimes this can work well and little or no other tweeking is needed. This does take a good vice with hardened jaws to do this job.
The other is to put the crank between dead centers in a Lathe and check the run out with an indicator, then decide which way it needs to be moved, then take a brass drift and hammer and tap the counter weight, fairly hard  to align the crank back within specs. This takes some practice and some are very hard to move. Just remove the dail indicator before you start wailing away or you will be buying a new one.
I try to get mine within .0005 or less but there are times they just won't come in any closer than .001 Which is well within specs. Myself I just want them as close as possible for less chance of vibrations and out of balance conditions.
All of these things rob HP and torque. If any one need father info or has questions please feel free to ask.
Richard.

Offline Cut4fun .

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Re: Making A Twin
« Reply #9 on: February 14, 2012, 01:27:35 pm »
Hello I am Jims friend in Idaho that is making this engine, Jim asked me about how to realign crankshafts.
I thought I would post this here for all to see.

Richard.

Welcome and Thanks for sharing info here.

You dont have to worry about me taking any crankshafts apart. But you never know about some of these other guys.
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